EFFECTS OF ESFENVALERATE POISE-EXPOSURE ON THE SURVIVAL AND GROWTH OFLARVAL AUSTRALIAN CRIMSON-SPOTTED RAINBOW FISH (MELANOTAENIA-FLUVIATILIS)

The effects of very short pulse-exposures with the synthetic pyrethroi d esfenvalerate on survival and growth of larval crimson-spotted rainb ow fish (Melanotaenia fluviatilis) were investigated in two series of experiments. Larval rainbow fish [2, 7, or 14 days (d) old] were pulse -exposed to esfenvalerate (30-700 ng L(-1)) for 1 h and then transferr ed to growth chambers where survival and growth were monitored for per iods of 7-28 d, depending on the experimental protocol. Mortality was found to be a more sensitive indicator of pesticide effects than growt h. Effects on growth were only observed in treatments where there was significant pesticide-related mortality. In these treatments, rainbow fish larvae were larger than control larvae. However, as increase in g rowth was always associated with mortality, it was not possible to det ermine if this was a direct effect of the pesticide or an artefact of density-dependent interactions within test populations. There was some evidence to suggest that pulse-exposure with esfenvalerate at an earl y age may cause subtle longterm detrimental effects to growth of larva l rainbow fish. Dry weight and condition (length/weight) were more sen sitive indicators of treatment effect than total length. Esfenvalerate was extremely toxic to larval fish, with 1 h pulse-exposures as low a s 60 ng L(-1) causing significant mortality. Newly hatched larvae were more sensitive to esfenvalerate than animals that were 14 d old. The effects of esfenvalerate on 7-d-old larvae could not be determined bec ause of high control mortality. Larvae of this age undergo transition from endogenous to exogenous feeding and may be more sensitive to hand ling stress. The lowest 1 h pulse-exposure esfenvalerate no observed e ffect concentration and lowest observed effect concentration were <60 and 60 ng L(-1) respectively, based on 2-d-old larval mortality. (C) 1 995 by John Wiley & Sons, Inc.